1. Field of the Invention
The present invention relates to a display control unit for transmitting display data to a display unit composed of a liquid crystal display (LCD), etc. on the basis of commands from a central processor. More particularly, the present invention relates to a display control unit and a display control method thereof suitably applied to devices requiring low power consumption such as a portable word processor and a personal computer, etc. operated by a battery.
2. Description of the Related Art
A personal computer, a word processor, etc. operated by a battery are developed to reduce power consumption such that the personal computer, the word processor, etc. can be operated for a long time.
For example, Japanese Patent Application Laying Open (KOKAI) No. 59-2081 shows a general technique for reducing power consumption of a display control unit. In this technique, power consumption is reduced by generally controlling each of display operations of a composite display plasma display panel (PDP) for providing a plurality of displays such as a segment display, a dot matrix display, etc. For example, Japanese Patent Application Laying Open (KOKAI) No. 2-292629 shows a control operation of the display control unit in which a central processor gets access to video RAMs. A speed of this control operation is increased by frequently changing addresses of the video RAMs when display data are accessed.
However, in such a general technique, no access control to the video RAMs is considered with respect to display data in which the same contents are continuously displayed. For example, characters are scattered as a whole when the characters are printed on the left-hand side of a document made by a word processor and blanks are formed on the right-hand side of the document. Characters are also scattered as a whole when table calculating soft or spreadsheet soft is used. In such cases, continuous dots often have the same color in a picture portion of a display unit. In the general technique, data are also read from the video RAMs with respect to such a picture portion in which the same color is continuously displayed, thereby consuming a large amount of power.
Accordingly, when display data are outputted to the display unit in the general technique, the video RAMs are accessed at any time irrespective of displayed contents, i.e., data contents of the video RAMs. Therefore, it is impossible to reduce power consumption of the display control unit by getting access to the video RAMs.